85
8.3 Skin
Appearance - together with knowledge of a substance and history of the individual, especially in the case of irritants.
Prick testing - A standardised solution of a substance is introduced just under the surface of the skin on a needle tip. A positive result is an 1mm or larger
wheal often with itch and flare within five minutes of the test. This is used to monitor immunological reactions to some respiratory allergens like the
enzymes used in biological detergents, or animal dander for those working in animal testing laboratories. The tests are also used to diagnose contact
urticaria. Prick testing can safely be used pre-employment when typically the standard series of grass pollen, fur, and house dust allergens are applied.
8.4 Breath
For example, Dichloromethane and carbon monoxide exposure.
8.5 Vision
Acuity tests Snellen and Keystone tests are applicable to the transport industry e.g. lorry drivers, pilots etc.
Colour blindness tests Ishihara test are applicable in jobs where colour matching is necessary, transport, HM forces, merchant navy, civil aviation,
railways, microscopy asbestos fibre analysis.
8.6 X-rays
Chest x-rays are useful for conditions such as infection e.g. TB, farmers lung, and pneumoconiosis. They are also routinely undertaken on asbestos
workers every two years. Pneumoconiosis chest x-rays are classified under the ILO international
classification system and compared with a standard set of films. Other X-Rays that may be used include Acro-osteolysis VCM and Divers.
8.7 Neurological tests
Mental function - IQ, dexterity, vigilance
86 Nerve transmission - Electromyography neuromuscular transmission and
Nerve conduction velocity Regular testing can prevent peripheral neuropathies by detecting very early changes.
Handwriting tests detects early tremors - mercury workers.
8.8 Audiometry
The lowest intensity at which a given pure tone can be heard is recorded. Values are expressed relative to a standard set of threshold values for normal
young people at specific frequencies these standards are set at 0 dB.
8.9 Lung function tests
8.9.1 Lung volume and Forced Expiratory Volume FEV1
Forced Vital Capacity FVC and Forced Expiratory Volume in 1-second FEV1 are measured using a spirometer for example, a Vitalograph, and
are then compared with predicted values. Predicted values depend on height, weight, sex, smoking, age and ethnic group. The subject blows through the
machine 5 times and an average of the last 3 or the 2 highest readings are accepted as correct.
8.9.2 Airways resistance
Peak expiratory flow rate - This is measured with a peak flow meter. It is used for monitoring potential changes due to respiratory allergens and for
diagnosing asthma and its response to treatment. Serial readings are sometimes taken every two hours.
87
9 GENERAL APPROACHES TO THE CONTROL OF RISKS TO HEALTH
The various steps taken to prevent or control the release of airborne contaminants, or propagation of some physical agents - in the work
environment are outlined and a range of examples given. These steps are commonly referred to as control measures and include combinations of
mechanical engineering and operationalprocedural systems aimed at preventing or minimising exposures.
Effective control is probably the single most important topic affecting health at work and underpins much of the legislative efforts designed to address health
protection at work. If an occupational hygiene assessmentsurvey identifies a risk to health, then
additionalimproved control measures need to be considered and implemented.
9.1 Types of Control Measures
Exposure prevention is the principal aim of any control strategy, particularly when handling hazardous agents, capable of producing serious irreversible
health effects; such as carcinogens and ionising radiation. In other cases, hazard effect, practicability, economics etc., may not require that all
exposures be prevented – exposure minimisation may be considered
sufficient. A hierarchical approach combining varieties of both engineering and
operationalprocedural control measures is universally accepted, and is presented below in decreasing order of desirability. In most cases effective
control strategies will utilise combinations of several, if not all of the measures listed.
88
Elimination Substitution
Isolation Segragation
Engineering Controls Including LEV Administrative Controls
Personal Protective Equipment
In c
re a
s in
g p
re fe
re n
c e
Source: Adrian Hirst
9.1.1 EliminationSubstitution
The most effective form of prevention control is simply to either eliminate the use of the hazardous agent, or the actual process in which it is used. This is
clearly not often practicable, but quite commonly hazardous agents or processes can be substituted with relatively innocuous ones, e.g.
Benzene replaced with toluene. Carbon tetrachloride replaced with methyl chloroform.
Talc replaced with chalk. Sand blasting replaced by steel shot blasting.
Dry handling techniques replaced by wet handling techniques. i.e.
suppression of dust emission e.g. removal of asbestos lagging.
9.1.2 Isolation
Wherever possible processes or operations, which involve some risks to health, should be completely enclosed, with the operators outside the
enclosure.
9.1.3 Segregation
Hazardous processes or operations etc. can be segregated from lower risk ones by placing them, for example, at the far end of a workshop, in a separate
89 room, or in a separate building, thereby minimising the number of workers at
risk.
9.1.4 Engineering Controls - Ventilation
Processes capable of producing exposures to hazardous substances only, are commonly controlled by the provision of mechanical air handling methods, of
either one of the two types below or a combination of both.
Local Exhaust Ventilation LEV
Local Exhaust Ventilation LEV - application of mechanical air handling techniques whereby potential airborne contaminants are captured near to the
source of emission, extracted, and discharged to either a safe location or subjected to some form of „air cleaning‟ technique. It is particularly valuable for
situations that involve a point source release of toxic contaminants.
General Dilution Ventilation
Dilution Ventilation - this is widely used throughout industry for the ventilation of control rooms, photographic laboratories, office spaces, mess-rooms and
printing rooms. It is not normally suitable for the control of dust, mist of fume or for substances of moderate to high toxicity, or in situations where the rate
of generation of contamination is non-uniform or high. Heating, Ventilation and Air Conditioning HVAC can also be used in a variety
of ways to control hazards associated with the thermal environment.
9.1.5 Administrative Controls
Administrative controls relate to how the interaction between personnel and the processoperation are organised. Great care is needed to ensure that
procedures, once adopted, are observed; particularly in the longer term, as shortcuts and non-
observance can become „custom and practice‟ over time, and once established can be difficult to overcome.
90 Sometimes the hazardous operation can be conducted during the evening or
night shift when fewer workers are around to be exposed. Job rotation is another method
of „protecting‟ personnel, through controlling work patterns. The worker can often influence the extent to which they are exposed to
airborne contaminants, e.g. for welding, via stance andor working upwind of the weld.
Housekeeping
Good housekeeping is particularly important in processes and laboratories where hazardous materials may be handled. Clear labelling, with relevant
health and safety advice, careful and appropriate storage and good work techniques all need to be addressed.
Handling of powders is a potentially hazardous operation and good housekeeping can help to minimise airborne contamination from spilled
materials, waste off-cuts etc. A cluttered or untidy workplace may also impede or prevent access to
essential system controls, such as LEV onoff switches, which could discourage their proper use. It can also make it difficult for workers to position
themselves correctly in relation to the task, thereby potentially risking greater exposures, and maybe even leading to problems associated with poor
ergonomics. Proper preventative maintenance schedules and regular inspectionleak
detection of process plant; plus frequent maintenance, examination and testing of engineering controls, such as LEV facilities, coupled with rapid
corrective actions where necessary, are essential if effective control is to be achieved and kept.
Personal factors are essential parts of all control strategies and are associated with the „management‟ aspects from both the perspective of how
the employer manages his employees, and how the employees „manage‟
themselves.
91
9.1.6 Information, Instruction and Training
Education of employees on any health hazards in the workplace and the importance of correctly using all the control measures provided, adopting
recommended operating procedures and wearing personal protection, if required, is needed in order to minimise the risks to health. Induction
courses, regular publicity, health and safety committees and positive line management can all play important roles in education.
Training of employees on the use of the appropriate control measures, operating practices etc., and the factors involved in the correct selection, use
and maintenance of personal protective equipment PPE. Fault reporting encouraging prompt communication, through appropriate
channels, of any problems encountered with the process, equipment, controls or PPE.
Good Hygiene Practices - these relate to the steps workers should take to protect their own health, and include following established decontamination
procedures, where applicable, regular laundering of clothing, using approved methodsfacilities; good personal hygiene
– frequent washingshowering particularly before meal breaks; and never eating, drinking or smoking within
designated process areas.
9.1.7 Personal Protective Equipment PPE
PPE is normally considered to be the last resort and only applicable when the preceding measures are insufficient or not reasonably practicable in
achieving a satisfactory work situation. Careful consideration must be given to the choice of the PPE device. It is important that the protection is effective
and comfortable; most personal protective equipment is not comfortable for extended use. Regular maintenance is vital for many types of PPE if effective
protection is be obtained. PPE management programmes need to be adopted whenever the option of PPE use is deemed necessary, and very pro-active
ongoing support to the programme will be required.
92
10 VENTILATION
The important features of ventilation systems are outlined, along with general principles associated with their design.
10.1 Types of Control
Local Exhaust Ventilation LEV is one of the most effective means available of preventing hazardous materials entering the workplace atmosphere. It
draws pollutants away from a process or operation that is likely to release a hazardous substance into the workplace. However, there are many cases
where the LEV is not effective and this may be as a result of poor design or lack of understanding of its proper use. LEV removes the contaminant at
source. Dilution Ventilation reduces the concentration of background contamination by
the addition of fresh, uncontaminated air. However, there is little, if any, removal or reduction of the contaminant at source.
10.2 General Features of an LEV System